Semi-automatic mechanical transmission control and control method

ABSTRACT

A control and control method for a semi-automatic mechanical transmission system (10) is provided for sensing operator request for a direct downshift into an optimum pull-away ratio and for automatically determining and engaging the optimum pull-away ratio.

RELATED APPLICATIONS

This application is a continuation-on-part of copending U.S. Ser. No.899,564, filed Aug. 22, 1986, which is a division of U.S. Ser. No.755,628, filed July 16, 1985, now U.S. Pat. No. 4,648,290, which claimspriority from British Provisional Patent Application No. 8418749 filedJuly 23, 1984.

BACKGROUND OF THE INVENTION

1. Field Of the Invention

The present invention relates to a control system and method for asemi-automatic mechanical transmission system, including a manuallyoperated shift selector, for automatically controlling the changing orshifting of transmission gear ratios on a vehicle, while leaving thevehicle driver or operator some residual measure of control. Inparticular, the present invention relates to a control system and methodfor the semi-automatic control of a mechanical change gear transmissionincluding means for automatically executing automatically determined anddisplayed allowable driver selected transmission ratio shifts, includingautomatic control of the vehicle master clutch in all but start fromstop situations. More particularly, the present invention relates to amethod of controlling a semi-automatic mechanical transmission wherein asingle downshift request made at a time when engine speed is below apredetermined reference engine speed is interpreted as a request for adownshift into the transmission ratio providing an engine speedapproximately equal to the midpoint between maximum governed enginespeed and peak torque engine speed.

2. Description of the Prior Art

Fully automatic transmission systems, both for heavy-duty vehicles suchas heavy-duty trucks and/or coaches, and for automobiles, that sensethrottle openings or positions, vehicle speeds, engine speeds, and thelike, and automatically shift the vehicle transmission in accordancetherewith are well known in the prior art. Such fully automatic changegear transmissions include transmissions wherein pressurized fluid isutilized to frictionally engage one or more members to other members orto a ground to achieve a selected gear ratio and automated mechanicaltransmissions utilizing electronic and/or pneumatic logic and actuatorsto engage and disengage mechanical (i.e. positive) clutches to achieve adesired gear ratio. Examples of such transmissions may be seen bereference to U.S. Pat. Nos. 3,961,546; 4,081,065 and 4,361,060, thedisclosures of which are hereby incorporated by reference.

Such fully automatic change gear transmissions can be unacceptablyexpensive, particularly for the largest heavy-duty vehicles which arenot typically sold in high volumes. Additionally, those automatic changegear transmissions utilizing pressurized fluid and/or torque converterstend to be relatively inefficient in terms of power dissipated betweenthe input and output shafts thereof. Moreover, many vehicle operatorslike to control the selection of the gear ratios, particularly sincethey can see and/or know the nature of the road ahead and/or of the loadbeing carried. Heavy-duty vehicles must often by accurately maneuveredinto restricted spaces at slow speeds, wherein fully automatictransmissions tend to only engage a given low gear. Particularly at suchtimes, when fuel metering to the engine is imperfect, as often happenstemporarily in any vehicle system, the vehicle operator tends to havedifficulty in performing delicate maneuvers with a fully automatictransmission, especially those not equipped with a manual clutch controlpedal, unless the operator is also utilizing the vehicle brake with hisleft foot.

The above drawbacks have been minimized by providing a semi-automaticmechanical transmission control wherein automatic changing between aplurality of gear ratios is provided while normally permitting thedriver to choose when to make a particular gear ratio change, whether toselect the immediately consecutive ratio up or down or to skip one ormore ratios, and when to slip, i.e. to incompletely engage, the vehiclemaster clutch in a low or crawler gear. Furthermore, the semi-automaticcontrol system prohibits engagement of a driver selected higher ratio,i.e. an upshift, that would cause the engine speed to decrease below theidle speed, i.e. would cause stalling and/or over-stressing at lowspeeds of the engine, and of a lower ratio, i.e. a downshift, if such achange would cause overspeeding of the engine. It is noted that withmanual mechanical transmissions such overspeeding of the engine canoccur due to a improper downshift even though the engine speed may begoverned against accelerating above the governed engine RPM. Examples ofsuch a semi-automatic transmission control can be seen by reference toallowed U.S. patent application Ser. No. 755,628 filed July 16, 1985,now U.S. Pat. No. 4,648,290.

While the above-described semi-automatic mechanical transmission controldoes provide a very desirable semi-automatic control, the control wassubject to improvement as, if the driver or operator desired a smoothshift into a strong pull-away gear after slowing of the vehiclesufficiently to cause engine speed in the current ratio to fall below anacceptable torque level, the driver was required to identify the desiredratio, to calculate the number of downshifts from the currently engagedratio to the desired ratio and to then move the selector lever thatnumber of times in the downshift direction.

SUMMARY OF THE INVENTION

In accordance with the present invention, the drawbacks of the prior artsemi-automatic mechanical transmission control have been minimized oreliminated by the provision of a control and control method which, ifthe vehicle is in motion and engine speed in the currently engaged gearratio has fallen to below an acceptable reference value, will interpret,and if allowable will execute, a single movement of the control lever inthe downshift direction as a request for a downshift directly into thegear ratio which, at current vehicle speed, will result in an enginespeed midway between maximum (governed) engine speed and peak torqueengine speed. In a typical diesel engine, the reference value will beabout 800 to 1200 RPM, while the desired or target engine speed afterthe downshift will be about 1700 to 1800 RPM to provide a smooth yetpowerful pull-away for a vehicle slowed by traffic and/or terrain.

Accordingly, it is an object of the present invention to provide a newand improved control method for semi-automatic mechanical transmissionhaving a control for automatically determining allowable up and downshifts from a given gear ratio, preferably for automatically displayingsame, and for automatically executing such permissible gear ratiochanges upon selector lever manual selection thereof by the vehicleoperator, wherein the operator can request an automatic selection of andshift into the optimal pull-away gear by a single movement of theselector lever.

Preferably, the semi-automatic mechanical transmission systemadditionally includes a manually operated vehicle master clutch operableby the vehicle operator during start from stop conditions, therebysimplifying the control of the automatic mechanical transmission systemand allowing the operator to slip the clutch during crawler maneuveringsituations.

This and other objects and advantages of the present invention willbecome apparent from a reading of the following description of thepreferred embodiments taken in connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the semi-automatic mechanicalchange gear transmission system of the present invention.

FIG. 2 is a schematic illustration of the control system of thesemi-automatic transmission of the present invention.

FIG. 3 is a perspective view of the driver's manual shift control anddisplay device.

FIG. 3B is an enlarged view of a portion of the display illustrated inFIG. 3.

FIG. 4 shows in block schematic form, the logic and control electronicsof the semi-automatic transmission control.

FIG. 5 illustrates the shift logic flow chart for a compound upshift.

FIG. 6 illustrates the shift logic flow chart for a splitter shift onlyupshift.

FIG. 7 illustrates the shift logic flow chart for a splitter shift onlydownshift.

FIG. 8 illustrates the shift logic flow chart for a compound downshift.

FIG. 9 is a schematic illustration, in the form of a flow chart, of thecontrol method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the present description of the preferred embodiment, certainterminology will be used for descriptive purposes only and is notintended to be limiting. The terms "upward", "downward", "rightward" and"leftward" will refer to directions in the drawings to which referenceis made. The terms "inward" and "outward", refer to directions towardsand away from, respectively, the geometric center of the device, orportion thereof, being described. The above applies to derivatives ofthe terms above specifically mentioned, and terms of similar import.

The term "simple transmission" is used to designate a change speedtransmission, wherein the operator may select one of a plurality ofsingle gear reductions. The term "compound transmission" is used todesignate a change speed transmission having a main transmission portionand an auxiliary transmission portion connected in series whereby theselected gear reduction in the main transmission portion may becompounded by further selected gear reduction in the auxiliarytransmission portion. The term "splitter type compound transmission" asused herein will designate a compound transmission wherein the auxiliarytransmission is used to provide various selectable steps forsubdivisions of the gear ratio selected in the main transmissionportion. In a splitter type compound transmission, the main transmissionsection is typically provided with relatively wide steps which are splitor subdivided by the auxiliary section. The term "upshift" as usedherein, shall mean the shifting from a lower speed gear ratio into ahigher speed gear ratio. The term "downshift" as used herein, shall meanthe shifting from a higher speed gear ratio to a lower speed gear ratio.The terms "low speed gear", "low gear" and/or "first gear" as usedherein, shall all designate the gear ratio utilized for lowest forwardspeed operation in a transmission or transmission section, i.e., thatset of gears having the highest ratio of reduction relative to the inputshaft of the transmission.

A "selected direction" of shifting will refer to selection of eithersingle or multiple upshifting or downshifting from a particular gearratio. The "displacement" between ratios refers to the number ofselectable ratios between two given ratios, for example, third speed orgear ratio is displaced by one (1) and two (2) ratios, respectively,from fourth and fifth speed, respectively, in the downshift direction.

The term "blocked transmission" or "blocked transmission section" shalldesignate a change gear constant mesh transmission or transmissionsection, wherein a selected one of a plurality of axially moveable gearsis nonrotatably coupled to a shaft as a result of axial movement of theselected gear from the neutral to the engaged position thereof, and bymeans of a resiliently biased positive clutch and a blocker is utilizedto prevent such engagement until the members of the positive clutch areat substantially synchronous rotation, such synchronous conditionachieved by manual and/or automatic manipulation of the transmissioninput and/or output shafts to cause a crossing of synchronous conditiontherebetween, but not typically achieved by frictional contact of theselected clutch members sufficient to cause one of the clutch members,and the apparatus associated therewith, to rotate with the other clutchmember. Blocked transmissions and/or transmission sections areillustrated in U.S. Pat. Nos. 3,799,002; 3,924,484; 4,192,196 and4,440,037, the disclosures of all of which are hereby incorporated byreference.

The present invention is applicable, in principle, to the semi-automaticcontrol of any type of mechanical change gear transmission adaptable forproviding output signals to and receiving command signals fromelectro-pneumatic control devices. However, the semi-automatic controlsystem of the present invention is particularly advantageously appliedto a splitter type compound transmission of the type having anon-synchronized, non-blocked main transmission section connected inseries with an auxiliary section of the blocked splitter type. Suchtransmissions are known in the prior art and are referred to as"semi-blocked" transmissions, and are described and illustrated inEuropean Patent Application No. 82303586.2, published Feb. 9, 1983 (No.EP-A-0071353) and European Patent Application No. 83307061.8, publishedSept. 5, 1984 (No. EP-A-0117342) disclosures of which publications arehereby incorporated by reference.

The semi-automatic transmission system to which the present invention isparticularly advantageously related, is described an illustrated inEuropean Patent application No. 85305072.2, published Feb. 5, 1986 (No.EP-A-0 170 465), the disclosure of which publication is herebyincorporated by reference.

Referring to FIG. 1, the position of a driver-operated throttle 24 issensed at sensor 22 and fed to a central processing unit 38, which alsoreceives inputs relative to engine speed from sensor 28 and/ortransmission input shaft speed from sensor 32, transmission output shaftspeed from sensor 36, and positive or negative actuations of thedriver's gear shift lever, or "joy stick" 1, to be described in greaterdetail below. It is understood that engine speed is an indication oftransmission input shaft speed, and visa versa, especially if clutch 16is nonslippingly engaged, while transmission output shaft speed is anindication of vehicle speed.

Control logic circuits, sensors, and actuators for the transmissionsystem 10 as disclosed in FIGS. 1 and 2, may be as disclosed in U.S.Pat. No. 4,361,060, the disclosure of which is hereby incorporated byreference. Specifically, central processing unit 38 receives inputs,processes same in accordance with predetermined logic rules, andprovides command output signals to pneumatic and/or electrical actuatorsfor control of an exhaust brake 17 and/or an input shaft brake 18 forrapid upshifts, and automatic fuel control 26 to "blip" the supply offuel to the engine 14 to achieve rapid synchronous rotation preparatoryto a downshift, clutch control via operator 30, and ratio shifting viatransmission operator 34. The central processing unit also sends commandoutput signals to the display 2 to be described in greater detail below.The semi-automatic transmission system 10 additionally comprises a usualfoot operated manual clutch control 3 intended for use only for startfrom rest and/or low speed creeping maneuvering situations. The control38 receives signals indicative of manual clutch control 3 position andof actuation of the vehicle brakes 4. The semi-automatic mechanicaltransmission system 10 also includes sources of electric and/orpneumatic power (not illustrated).

As used herein, the term "blip" designates a temporary increase in thesupply of fuel to the engine 14, while the term "dip" means a momentarydecrease in supply of fuel to the engine. The terms blip and dip areusually associated with automatic controller 38 commanded increases anddecreases, respectively, of the supply of fuel to the engine independentof the operator selected position of manual throttle pedal 24.

Preferably, as may be seen by reference to FIG. 3, the centralprocessing unit 38 may be contained in a box or housing 38A, whichhousing carries the display panel 2 having an upshift indicator display2', a downshift indicator display 2", and a currently engaged gear ratiodisplay 2"', the shift select lever 1, an optional reverse enable button1A, as well as a central processing unit electronic circuitry 38B.

The schematics of the control system of the semi-automatic mechanicaltransmission system 10 are also illustrated in FIG. 2.

Referring to FIG. 3B, the display 2 includes upshift indicator section2', downshift indicator section 2" and currently engaged gear ratioindicator section 2"'. As illustrated, the currently engaged gear ratiodisplay section 2"' is presently displaying a "6" indicating that thevehicle transmission is operating in sixth (6th) gear. The upshiftdisplay section 2' has three lines indicating the maximum number ofpermissible consecutive upshifts permitted according to the sensed inputparameters, such as sensed engine or input shaft speed and sensed outputshaft speed as processed according to the predetermined logic rules orprogram. In the present situation, the three lines indicate that asingle, a double or a triple upshift is permissible. Accordingly, thedriver may select a permissible shift directly to either seventh (7th),eighth (8th) or ninth (9th) speed. The downshift display 2" section hastwo lines indicating the maximum number of permissible consecutivedownshifts permitted according to the sensed parameters as processed bythe predetermined logic or program. In the present situation, the twolines in display 2' indicate that the transmission may be permissiblydownshifted to either fifth (5th) or to fourth (4th) gear.

Briefly, the permissibility of a possible upshift or downshift isdetermined by comparing the expected engine speed at the completion ofsuch an upshift or downshift, assuming a substantially constant vehiclespeed and fully engaged master clutch, to a fixed range of maximum andminimum permissible engine speeds. The central processing unit 38 willnot issue command signals to execute a selected impermissible ratiochange. Preferably, a central processing unit will execute the closestpermissible ratio change to that selected by the operator. By way ofexample, assuming the conditions indicated by display 2 as illustratedin FIG. 3B, should the operator select a downshift to third gear, such adownshift will not be executed by the central processing unit 38 asbeing impermissible. However, in the preferred embodiment, the centralprocessing unit 38 will issue command output signals for a doubledownshift from sixth gear to fourth gear. Not only is an impermissibleratio change refused, but the driver will usually have been advisedalready by display 2 that the ratio should never have been attempted orselected.

The display 2 provides an indication to the operator what upshifts anddownshifts are permitable and as to which upshifts and downshifts areimpermissible. Should the driver not heed the warning, the centralprocessing unit 38 will not generate impermissible shift command eventhough synchronization of the mechanical jaw clutch elements could beobtained by the system.

When the upshift indication display 2' is blank, no upshift is allowedand the driver is probably driving at a very low economical engine RPM.Conversely, when the downshift indicator 2' is blank, i.e. has nohorizontal lines displayed therein, no downshift is allowable, andmaximum torque, acceleration or hill climbing will probably already beavailable in the system in its current engaged gear ratio. Gear shiftsare always achieved without the operator manually engaging and/ordisengaging the master clutch 16 by means of the mechanical manualclutch pedal 3, which is normally only used for starting from rest,reversing or for maneuvering in warehouses, etc., as vehicle clutcheshave traditionally been used.

To shift transmission 12, the driver moves lever 1 forward (forupshifts) and rearward (for downshifts) from the position illustrated inFIGS. 2 and 3. To select a single upshift, i.e. a shift to seventh gear,the operator will move lever 1 forward once and the lever will thenreturn to the neutral or centered position under bias. If, in sixth gearas shown, the operator moves the lever forward three times in quicksuccession, each allowing its return to rest, he will skip two gears ineffect, and achieve a skip shift directly into ninth speed (i.e. seventhand eighth speeds will not be engaged) almost instantaneously.Accordingly, multiple or skip shifts may be commanded by use of thesemi-automatic control of the present invention. The declutching of themaster clutch 16 and synchronizing of the selected jaw clutch membersassociated with the selected gear ratio is achieved automatically andrapidly due to automatic throttle and clutch control and braking of theinput shaft and/or the engine. The control system is semi-automatic andthe driver must exercise his discretion as to when to up or downshift,and as to how many gear ratios to up or downshift, but is not calledupon to coordinate gear lever, throttle pedal and clutch actuation. Oncethe driver has selected a permitted gear ratio, the throttle is blippedto achieve necessary synchronization during a downshift, or dipped forachieving necessary synchronization during an upshift, all of which isdone automatically for the driver by the central processing unit 38. Thereverse mode of operation may be achieved only from the neutral at restposition and then is achieved by moving control lever 1 backwardly fromthe currently engaged neutral position. To prevent and inadvertent"downshift" into reverse, a reverse button 1A may be provided whichbutton must be depressed prior to the central processing unitinterpreting a backward movement of the control lever 1 when in theneutral position as a request for reverse operation.

Upshifts and/or downshifts involving both the main and auxiliarysection, i.e. compound shifts, are equally simple for the driver toachieve as are those involving only the auxiliary section, i.e. a splitshift. In those transmissions provided with multiple reverse gearratios, the transmission may be downshifted into lower reverse ratiosand upshifted into higher reverse ratios by movement of the controllever backward and forward as indicated. Of course, any type of toggleswitch or button which may be located on the end of the shift lever maybe utilized in place of reverse enable button 1A.

It is understood that a single control lever moveable forward andbackward in a given direction to select a forward and reverse mode ofoperation, and then moveable in a transverse direction to selectupshifts and downshifts either single or multiple, of the type disclosedin U.S. Pat. No. 4,442,730, the disclosure of which is herebyincorporated by reference, may be substituted for the control lever 1illustrated.

It is another important and advantageous feature of the semi-automaticcontrol system of the present invention that, whenever the vehicle isbrought to a complete stop, the clutch 16 is manually disengaged bymeans of foot pedal 3 and the lever 1 is moved in the downshiftdirection once, the control will automatically shift transmission 12 toa preselected, preferably the highest permissible, starting gear ratio,which may involve skip-shifting over a large plurality of interveninggear ratios. By way of example, in a twelve forward speed transmission,the highest permissible starting ratio may be third gear. Another levermovement in the downshift direction would the shift the transmission tosecond for a quicker or slightly uphill start, etc. The operator, atrest or in motion, can always select a gear ratio from those permitted.The manual clutch is only intended for use preparatory to stopping todisengage the transmission and avoid stalling and during starting fromrest in any of the permissible starting gear ratios. If, during asemi-automatic shift, if the driver operates the manual clutch, thein-process gear change will be interrupted and will only continue uponre-engagement of the manual clutch.

As an optional feature, if in an emergency situation, such as duringevasion of an obstacle in the road etc., the operator stops the vehiclewithout de-clutching the manual clutch, the very low road speed issensed and the clutch 16 may be automatically disengaged. Such anautomatic de-clutching procedure will prevent stalling of the engine,thus retaining steering and other engine driven powered functions. Toagain place the vehicle in motion, the operator will manually disengageclutch 16 and move the gear lever 1 in the downshift direction to againselect the highest permissible starting ratio. Preferably, transmission12 is a multi-speed transmission having at least five, preferably nineor more, selectable forward ratios.

The structure of a twelve forward speed splitter type transmission 12,and of the blocked jaw clutch members utilized in the auxiliarytransmission section of transmission 12, is known in the prior art andmay be appreciated in greater detail by reference to above mentionedU.S. Pat. Nos. 3,799,002; 3,921,469; 3,924,848; 4,194,410; 4,440,037;and to published European Patent Application Nos. EP-A-0071353 andEP-A-0117342.

The typical operation of the permissible ratio determination procedureand ratio change operating of the control system of the invention arenow further explained.

The functions and components for the semi-automatic transmission are,gear ratio change selection switch or lever 1, display panel 2, controlbox 38, speed sensors 32, 36, engine (fuel) control 26, throttle andclutch sensors 22, 3 (detecting the driver's depression of them),electro-pneumatic control of shifts, clutch and brakes (using the enginemanifold vacuum, together with a vacuum servo-follower if required), theinput brakes 17 and/or 18 and their actuators, control cables, and theclutch actuator 30.

Referring to the items 1, 2 and central control unit 38, these input thedriver's change requirements, tell him what gear he is in, which otherratios he can choose at any moment, including from rest, from sensedengine and vehicle status necessary to complete any gear shifts, eithersingle or skip. Shifting is accomplished by the single or pluralmovement of the gear level 1, either forwards for up shifts or backwardsfor down shifts. The gear shift lever is spring biased to return to therest or vertical position and one movement of the lever will instigateone shift control.

Control of the engine is by fuel control 26 which includes two (2)solenoid valves, one associated with the engine "dipping" and the otherwith engine "blipping". Dipping is used not only for up changes, butalso preparatory to down changes to break the torque line. Aback-to-back double pneumatic piston, which is slaved to the solenoidvalves, provides servo pump manipulations, if desired without driverfeel. These units respond to signals from the electronic panel. A"fly-by-wire" throttle control or full electronic engine management canbe accommodated by the system.

In order for the system to function correctly it is necessary toidentify the existence of full clutch and part-throttle actuations, thiswill be achieved by the placement of switches (micro or proximity) atleast at the full extends of the clutch and initial acceleratormovements from the driver's foot pedals.

The transmission operator 34 includes an electro pneumatic ("EP")manifold is preferably broken down into two elements. The firstassociated with the front box and the second with back box operations.The EP manifold is a manifold controlled by solenoid valves andassociated with the cylinders carrying the shift pistons.

The operator 34 also includes a shift unit with comprising air pistonsmoved by the servo operation of the appropriate EP valve as it issignaled from the electronic control box 38.

The driver could be instructed as follows: The vehicle will bestationary, air pressure at the right level, hand brake on, clutchdisengaged and acceleration at idle. Neutral will be indicated in thedisplay unit. The driver will move the gear lever forward once, thuspre-disposing the unit to start in the lowest ratio. No engagement hasyet been made. The clutch pedal will be depressed and the micro switchbecomes actuated at the extent of the travel.

With the engagement of first gear, the release of the clutch pedal andapplication of the throttle when the hand brake is released, the vehiclewill move and normal acceleration follows. At the desired speed thedriver may then select the next highest ratio by a single manipulationof the gear lever forwards. At zero speed one movement of the lever willreturn the gearbox to a starting gear from its status when the vehiclehas come to rest.

The visual indication will be in such a position that the appropriategear is shown without the need for the driver to divert fully hisattention from the road ahead. The electronic panel, including CPU 38,receives the driver's commands from the gear selector unit, speedsignals from the gearbox input and output shafts and will send commandsto the EP manifold, shift unit, up shift inertia brake, engine andclutch control such that semi-automatic shifting is accomplished.

Control of the engine occurs in two (2) elements. The electronics willexamine the condition between the transmission input and output shaftspeeds and if an upshift is possible, an automatic firing of thethrottle, clutch and upshift brake controls will take place givingsynchronization and an engagement of second gear. Following theengagement of second, the upshift brake will be released (prior releasemay be initiated if required), and the clutch and engine controlsrestored to the status quo. The sequence, because it is automatic, willbe so rapid that a minimum of loss of vehicle performance will benoticed and it will be almost impossible for the vehicle to move from astate of go to a state of no go. As could happen if the throttlemanipulation was slaved to the whim of the driver. This sequence may berepeated up through the box as conditions allow until the highest ratiois reached.

Down shifts are required as the engine and vehicle speed decrease underadverse load/road conditions and a down shift may be requested at anytime. The fulfillment of the shift, however, can only be achieved ifsufficient engine speed range is available to achieve synchronization.Assuming that the conditions pertaining are current, then one of twosequences will occur. The sequence utilized is dependent upon the changebeing a back box only shift or a compound shift involving both front andback box.

Split shift--auxiliary section only

With the signal for a single back box shift the gear in the back boxwill be selected and the "throttle dip" (fuel pump towards idle)sequence initiated for a time sufficient to break the torque line andallow disengagement. The clutch also will be disengaged and thenre-engaged. The "throttle dip" sequence will be ended and a period of"throttle blip" (fuel pump towards full throttle) commences. At thedetection of synchronous the splitter mechanism will activate engagingthe lower gear, the "throttle blip" period will end and the throttlerestored to the state demanded by the driver.

Compound shift--main and auxiliary section

For a compound (main and auxiliary section change) shift. The sequenceis only marginally different. The sequence up to and including the firstclutch disengagement remain the same, but then the following sequenceensues. Neutral is selected in the front box while the clutch is stilldisengaged for an appropriate time period. The clutch is thenre-engaged, the "throttle dip" signal removed and the throttle blipactivated. At the detection of synchronous, the throttle blip is endedand following an appropriate delay period, the front box engagement ismade.

The above sequences are illustrated in the flow charts of FIGS. 5-8.

ELECTRONICS TO ACHIEVE THE ABOVE FLOW CHARTS

Electronics are used to control the pneumatic control lines to the shifthousing, engine speed, clutch and inertia brake operators. It alsoinhibits non-allowable gear changes and gives a display of present gearand gear(s) available for shifts. The inputs that the electronicsrespond to are gear lever demand signals, input shaft speed, outputshaft speed throttle threshold position and clutch pedal position(whether depressed or not). The electronics are shown is in schematicblock form in FIG. 4. The actual value road speed signals frequency ismeasured and respective set value binary numbers created that representthe maximum speeds available in all gears i.e. Binary 1 will occur atthe maximum speed in first gear up to binary 11 which will occur atmaximum speed available in eleventh gear.

This actual road speed binary number has a binary 3 added to it and boththis added value and the actual speed binary are taken to two binarycomparators, the other input of which comes from the present actualgear. The other input to each comparator has responded to the registeredgear ratio engaged, to be supplied with the respective set value maximumspeed binary. The effects of this is to create a "window" of availablegears at any one actual road speed. Should the "demanded" gear beoutside this window, then the selection is nullified by gates as will bedescribed later. To take two examples, of this, at zero actual speedonly gears 1, 2 and 3 will be available. At maximum actual speed in,say, second gear only gears 3, 4 and 5 will be available.

The "present" (or actual) gear selection binary comes from the outputsof a bidirectional 4 bit counter. An upshift demand causes the counterto increase and a downshift demand causes it to decrease. There aregates in the input which are closed if the "demanded" gear is outsidethe window. Should the required selection be outside the window becausethe speed is too low for the demanded down change, then the vehicle willchange down further to the highest permissible gear.

Each upward shift will also initiate a Throttle Dip (TD) and eachdownward change will produce a Throttle Blip (TB). These will continueuntil the engine is synchronized with the road speed which will then cutoff the respective TD or TB and select the next gear. See also thepreceding flow charts.

Thus, it will be seen that the gear changes in the preferred embodimentsdo not depend on torque, although that could be built in. They arepermitted in dependence only on the starting and finishing speeds, andon the actual gear engaged and the possible selected ratio.

It is emphasized that compared with a fully automatic transmission, thepresent semi-automatic transmission provides driver control anddiscretion, particularly advantageous at very low speeds and where theterrain or road conditions ahead may be difficult. He does not need touse the throttle and clutch to change ratios, except when starting fromrest, or maneuvering. A cruise control or a governed top road speedcould easily be incorporated in the control box 38. The driver feelsnegligible feedback on his foot when the throttle is being operated forshifts. The shifts are very rapid, so that the displayed condition ofpermissible shifts (e.g. skipping two ratios on an upshift) does notchange during the brief time of the shift, the vehicle not appreciablyslowing down. A normal synchromesh or nonsynchronized mechanical changegear gives no protection for the engine racing, or laboring at idlespeeds after a misjudged but allowed and completed change.

As an additional feature, as illustrated in FIG. 9, if the operatorallows the vehicle engine speed to fall below a reference value (such asthe minimum engine speed providing acceptable torque level, such asbelow 800-1200 RPM for a typical heavy duty vehicle diesel engine) whilethe vehicle is in motion; as might occur in a congested trafficsituation, or upon approaching a traffic circle or upon a hill; a singlemovement or pulse of lever 1 in the downshift direction will beinterpreted as a request for automatic selection and engagement of anoptimum pull-away ratio.

Briefly, an optimum pull-away ratio is that ratio which, at expectedvehicle speed after completion of the downshift and reengagement of themaster clutch (as a practical matter, this is generally equal to currentvehicle speed) will result in an engine speed approximately midwaybetween the maximum permitted (usually the governed) engine speed(usually governed at about 2100 RPM) and the peak torque speed of theengine. For a typical diesel engine, the target engine speed is about1700-1800 RPM.

By the above procedure, the vehicle operator can, with relative ease,request automatic selection and engagement of a transmission ratioproviding relative smooth vehicle operation and good vehicle performancefor pulling away from a temporary traffic slowdown.

Although the preferred embodiment of the present invention has beendescribed with a certain degree of particularity, various changes toform and detail may be made without departing from the spirit and scopeof the invention as hereinafter claimed.

We claim:
 1. A method of controlling a semi-automatic mechanical changegear transmission system (10) comprising a manual fuel throttle control(24), a fuel throttle controlled engine (14), a multi-speed change gearmechanical transmission (12), a friction master clutch (16) interposedthe engine and transmission, a manually operated shift selection lever(1) moveable in a first direction from a centered position to selectupshifts and in a second direction from said centered position to selectdownshifts from the currently engaged gear ratio, a central processingunit (38) for receiving inputs indicative of transmission input shaftand output shaft rotational speeds, of vehicle speed, of engine speed,of currently engaged ration and of operation of said shift selectionlever and for processing same according to predetermined logic rules toissue command output signals to non-manually controlled operatorsincluding a clutch operator (30), a fuel throttle control operator (26),and a transmission operator (34), said processing unit sensing operationof said manual shift selection lever including the direction of movementthereof and a number of displacements of said lever within apredetermined period of time from said centered position, said methodcomprising the steps of: determining in a first mode of operation atransmission gear ratio selected by the operator to be shifted directlyinto from the currently engaged ratio by assuming each repetition ofdisplacement from the centered position of said shift selection lever ina given direction indicates operator selection of a change of oneadditional consecutive ratio in said direction, andselectingautomatically in a second mode of operation interpretation of a singledisplacement of said shift selection lever from the centered position inthe second direction as an operator selection of a downshift directlyinto an optimum pull-away transmission ratio if vehicle speed is greaterthan a predetermined vehicle speed reference value and engine speed isless than a predetermined engine speed reference value.
 2. The method ofclaim 1, wherein said optimum pull-away ratio is the transmission ratiowhich, at expected vehicle speed after completion of a shift, willresult in said engine rotating at an engine speed approximately midwaybetween a predetermined maximum allowable engine speed and a peak torquespeed of the engine.
 3. The method of claim 2, wherein said engine is adiesel engine having a maximum governed speed, said predeterminedmaximum allowable speed equaling said maximum governed speed.
 4. Themethod of claim 2, wherein said predetermined engine speed referencevalue corresponds to the engine speed below which engine torque lessthan a minimum acceptable value.
 5. The method of claim 4, wherein saidminimum acceptable torque value is about thirty percent of peak enginetorque.
 6. The method of claim 3, wherein said predetermined enginespeed reference value corresponds to the engine speed below which enginetorque less than a minimum acceptable value.
 7. The method of claim 6,wherein said minimum acceptable torque value is about thirty percent ofpeak engine torque.
 8. The method of claim 2, wherein said engine is adiesel engine having a maximum governed speed of about 2100 RPM, saidengine speed reference value is about 1000 RPM and said engine speedmidway between maximum allowable speed and peak torque speed is about1750 RPM.
 9. The method of claim 3, wherein said engine is a dieselengine having a maximum governed speed of about 2100 RPM, said enginespeed reference value is about 1000 RPM and said engine speed midwaybetween maximum allowable speed and peak torque speed is about 1750 RPM.10. The method of claim 2 wherein, in said first mode of operation, saidprocessing unit is effect to process said input signals to determine thecurrently engaged gear ratio of said transmission and to determinepermissibly engaged gear ratios of said transmission under sensedvehicle operating conditions andto issue command output signals to causean automatic upshift or downshift from the currently engaged gear ratioto the least displaced gear ratio from currently engaged gear ratio of(1) the operator selected gear ratio or (2) the most displaced fromcurrently engaged ratio of the permissible gear ratios in the selecteddirection of shifting, said command output signals causing saidtransmission to be shifted directly from said currently engaged gearratio to said least displaced gear ratio.
 11. The method of claim 4wherein, in said first mode of operation, said processing unit is effectto process said input signals to determine the currently engaged gearratio of said transmission and to determine permissibly engaged gearratios of said transmission under sensed vehicle operating conditionsandto issue command output signals to cause an automatic upshift ordownshift from the currently engaged gear ratio to the least displacedgear ratio from currently engaged gear ratio of (1) the operatorselected gear ratio or (2) the most displaced from currently engagedratio of the permissible gear ratios in the selected direction ofshifting, said command output signals causing said transmission to beshifted directly from said currently engaged gear ratio to said leastdisplaced gear ratio.
 12. The method of claim 5 wherein, in said firstmode of operation, said processing unit is effect to process said inputsignals to determine the currently engaged gear ratio of saidtransmission and to determine permissibly engaged gear ratios of saidtransmission under sensed vehicle operating conditions andto issuecommand output signals to cause an automatic upshift or downshift fromthe currently engaged gear ratio to the least displaced gear ratio fromcurrently engaged gear ratio of (1) the operator selected gear ratio or(2) the most displaced from currently engaged ratio of the permissiblegear ratios in the selected direction of shifting, said command outputsignals causing said transmission to be shifted directly from saidcurrently engaged gear ratio to said least displaced gear ratio.
 13. Acontrol for a semi-automatic mechanical change gear transmission system(10) comprising a manual fuel throttle control (24), a fuel throttlecontrolled engine (14), a multi-speed change gear mechanicaltransmission (12), a friction master clutch (16) interposed the engineand transmission, a manually operated shift selection lever (1) moveablein a first direction from a centered position to select upshifts and ina second direction from said centered position to select downshifts fromthe currently engaged gear ratio, a central processing unit (38) forreceiving inputs indicative of transmission input shaft and output shaftrotational speeds, of vehicle speed, of engine speed and of operation ofsaid shift selection lever and for processing same according topredetermined logic rules to determined currently engaged gear ratio andto issue command output signals to non-manually controlled operatorsincluding a clutch operator (30), a fuel throttle control operator (26),and a transmission operator (34), logic rules causing said processingunit in a first mode of operation, to determine the transmission gearratio selected by the operator to be shifted into from the currentlyengaged ratio by assuming each displacement from the centered positionof said shift selection lever in a given direction indicates operatorselection of a change in ratio in said direction and in a second mode ofoperation causing said processing unit to interpret a singledisplacement of said shift selection lever from the centered position inthe second direction as an operator selection of a downshift directlyinto an optimum pull-away ratio if vehicle speed is greater than apredetermined vehicle speed reference value and engine speed is lessthan a predetermined engine speed reference value.
 14. The control ofclaim 13, wherein said optimum pull-away ration is a transmission ratiowhich, at expected vehicle speed after completion of a shift, willresult in said engine rotating at an engine speed approximately midwaybetween a predetermined maximum allowable engine speed and a peak torquespeed of the engine.
 15. The control of claim 14, wherein said engine isa diesel engine having a maximum governed speed, said predeterminedmaximum allowable speed equaling said maximum governed speed.
 16. Thecontrol of claim 14, wherein said predetermined engine speed referencevalue corresponds to the engine speed below which engine torque lessthan a minimum acceptable value.
 17. The control of claim 16, whereinsaid minimum acceptable torque value is about thirty percent of peakengine torque.
 18. The control of claim 14, wherein said engine is adiesel engine having a maximum governed speed of about 2100 RPM, saidengine speed reference value is about 1000 RPM and said engine speedmidway between maximum allowable speed and peak torque speed is about1750 RPM.